This invention relates to DC voltage regulators including a voltage-reference circuit and more particularly to such a regulator that further includes a means for preventing damage to the regulator from high transient voltages that may superimpose on the DC supply voltage.
A prior art voltage regulator circuit is shown in FIG. 1. It is formed in an integrated silicon circuit chip 10 having a ground terminal 12 and a DC supply voltage terminal 14 to which a DC voltage, +V.sub.cc, may be applied. A regulated voltage, V.sub.REG, is provided at output conductor 16 to which a load (not shown) may be connected.
This circuit includes a constant current source circuit 20 made up of transistors 21, 22 and 23 plus resistors 24 and 25. Also included is a current mirror circuit 27 consisting of transistors 28 and 29. The constant current 19 provided by the constant source current 20 is mirrored through current mirror 27 to provide a bias current 31 that serves as base bias for transistor 30. The series regulating pass transistor 30 drops the voltage from V.sub.cc to V.sub.reg.
The band-gap regulator 32 senses the output voltage at conductor 16 and compares it to an internally generated constant voltage reference and diverts or sinks enough of current 30 to maintain the voltage at the desired level V.sub.reg over wide ranges of load current and source voltage V.sub.cc. A first such circuit is described in the article "New Developments in IC Voltage Regulators", IEEE Journal of Solid State Circuits, Vol. SC-4, pp. 2-7, February 1971, by R. J. Widlar.
There have been combined with these kinds of voltage regulator circuits a variety of protective circuits. For example, a zener clamp may be connected across the pass transistor to prevent reverse breakdown of that transistor. In that case, it will be necessary to place such a clamp across the load as well. Also, current limiting circuits have been added to limit the pass transistor current to a safe value.
It is an object of this invention to provide a simple voltage regulator circuit having a protective means for preventing damage to the regulator circuit resulting from large voltage transients superimposed on the supply voltage.